Concerning the promotion of peripheral collateral growth, clinical studies investigating new therapeutic strategies have used imprecise assessment methods and therefore determined only "weak" endpoints. In contrast to the coronary circulation, there is currently no gold standard available to document successful promotion of collateral growth in patients suffering from peripheral artery disease. Therefore, the purpose of this study is to evaluate a new invasive method to quantify arterial collateral flow in the lower extremity in patients undergoing elective coronary angiography.